The computeIfPresent(Key, BiFunction) method of HashMap class which allows you to compute value of a mapping for specified key if key is already associated with a value (or is mapped to null).
- If mapping function of this method returns null, the mapping is removed.
- If the remapping function throws an exception, the exception is rethrown, and the mapping is left unchanged.
- During computation, modification this map using this method is not allowed.
Syntax:
public Object computeIfPresent(Object key,
BiFunction remappingFunction)
Parameters: This method accepts two parameters:
- key: key with which the value is to be associated.
- remappingFunction: function to do the operation on value.
Returns: This method returns new remapped value associated with the specified key, or null if mapping returns null.
Below programs illustrate the computeIfPresent(Key, BiFunction) method:
Example 1: This example demonstrates the case when the key is not in the hashmap.
// Java program to demonstrate// computeIfPresent(Key, BiFunction) method.  import java.util.concurrent.*;import java.util.*;  public class GFG {    public static void main(String[] args)    {          // Create a HashMap and add some values        HashMap<String, Integer> wordCount = new HashMap<>();        wordCount.put("Geeks", 1);        wordCount.put("for", 2);        wordCount.put("geeks", 3);          // print HashMap details        System.out.println("Hashmap before operation :\n "                           + wordCount);          // provide new value for keys which is present        // using computeIfPresent method        wordCount.computeIfPresent("Geek",                                   (key, val) -> val + 100);          // print new mapping        System.out.println("HashMap after operation :\n "                           + wordCount);    }} |
Output:
Hashmap before operation :
{geeks=3, Geeks=1, for=2}
HashMap after operation :
{geeks=3, Geeks=1, for=2}
Example 2: This example demonstrates the case when the key is present in the hashmap.
// Java program to demonstrate// computeIfPresent(Key, BiFunction) method.  import java.util.concurrent.*;import java.util.*;  public class GFG {    public static void main(String[] args)    {          // Create a HashMap and add some values        HashMap<String, Integer> wordCount = new HashMap<>();        wordCount.put("Geeks", 1);        wordCount.put("for", 2);        wordCount.put("geeks", 3);          // print HashMap details        System.out.println("Hashmap before operation :\n "                           + wordCount);          // provide new value for keys which is present        // using computeIfPresent method        wordCount.computeIfPresent("for",                                   (key, val) -> val + 1);          // print new mapping        System.out.println("HashMap after operation :\n "                           + wordCount);    }} |
Output:
Hashmap before operation :
{geeks=3, Geeks=1, for=2}
HashMap after operation :
{geeks=3, Geeks=1, for=3}
